A draft shield is an important element particularly in balances that are designed to weigh the most minute loads, for example in the microgram range or even in the sub-microgram range, because in these load ranges the smallest changes for example in the air flow, the buoyancy, or due to temperature changes and/or shocks can have a significant influence on the weighing result. To minimize these influences, it is usually necessary, after a weighing object has been placed on the balance, that the actual weighing is carried out with a certain time delay to allow primarily the air enclosed in the weighing compartment to come to rest and to also ensure that all other extraneous parameters are as constant as possible. This improves the measurement accuracy, but the time interval for a measurement is considerably lengthened, so that in particular multiple measurements or verification measurements of weighing loads or weighing objects of the same kind will take an unduly long time.
Furthermore, when placing a weighing object on the balance, care should be taken to avoid putting any additional pressure or force on the load carrier when the load is placed on the balance, as the load carrier is connected to the weighing mechanism and the latter can be damaged or even destroyed by an excessively strong and/or uncontrolled application of force. For example, if the load is put manually on a highly precise balance by means of a pair of tweezers, the repeatability of a measurement can be influenced, because the mechanical forces applied or generated are of different magnitude every time a load is placed on the load carrier.
Electronic balances of the known state of the art, for example laboratory balances, analytical balances or microbalances are equipped with different versions of draft shields depending on the area of application, in substantially angular as well as round configurations, which normally have at least one access opening through which the load is put on the balance and which can in most cases be closed.
One application among others for high-precision balances, so-called microbalances, is for check-weighing small tube- or rod-shaped weighing objects, such as for example stents for vascular surgery applications. In applications of this kind, as many objects of the same type as possible need to be weighed one after another in the shortest possible time. Other applications can include for example also the check-weighing of certain articles or the monitoring of weight fluctuations of one or more weighing objects over a certain time span, for example in quality assurance.
High-precision balances are no longer used exclusively in the laboratory but to a growing extent also in the serial production of very small articles such as stents, filters, implants, computer chips and the like. In particular in production, a balance must meet on the one hand the requirement that it guarantees the required measurement accuracy and rapidly delivers reproducible results, while on the other hand it has to be robust and simple to operate.
The requirements imposed on the design of the balance and in particular on parts that can be brought into contact with a weighing object, are becoming constantly more stringent, particularly in areas of application that are subject to strict legal constraints, such as for example in medicine, biochemistry, or in pharmaceutics. One of these requirements is for example that the parts of the balance that come into contact with a weighing object, in particular the weighing compartment, are easy to clean.
It is for example possible that a closure element which serves to open or close the weighing compartment, or also the inside of the weighing compartment, come into contact with the weighing object, for example if the weighing object falls off the load-receiving device or, in the process of being brought into the weighing compartment, comes into contact with the closure element.
It would therefore be advantageous if these components, too, could be easily cleaned and cleared of residues through physical and/or chemical methods, as well as sterilized if necessary, so that they satisfy at least the legal requirements for cleanliness and/or hygiene in different fields of application.